1. Field of the Invention
The present invention relates to a device for recording and/or reproducing digital data having a plurality of kinds of rates, and a method for reproducing the same.
2. Description of the Related Art
In recent years, various kinds of digital video cassette recorders (hereinafter, referred to as DVCRs) for recording video signals such as TV signals in digital form have been developed. However, since video signals contain a great amount of information, in the case where the video signals are recorded in digital form in a storage medium such as a tape, a long recording time is required. In view of such a problem, a method for recording video signals, which are subjected to high efficiency coding, in digital form has been proposed, for example in the International Conference on Consumer Electronics (ICCE) Jun. 6-9, 1989, Digest of Technical Papers WPM8.6 "AN EXPERIMENTAL STUDY ON A HOME-USE DIGITAL VTR".
In the past, DVCRs record input video signals in synchronization with a field frequency thereof. More specifically, a magnetic head mounted in a rotary cylinder rotating in synchronization with the field frequency records video signals in tracks each having a track angle predetermined in accordance with set standards.
DVCRs use a rotary cylinder for the purpose of enhancing a recording density, and record data in tracks so as to be disposed on a magnetic tape in the diagonal direction of a magnetic tape traveling direction. For example, when a magnetic tape is wrapped around a rotary cylinder provided with two magnetic heads by about 180 degrees and the rotary cylinder rotates at a speed of 9000 rpm (rotation per minute), 18000 tracks are recorded on the magnetic tape per minute.
In general, DVCRs reproduce data in the same state as in the recorded state, except for special reproduction such as scene search, still, and slow reproductions. If data is reproduced in the state different from the recorded state, normal reproduction cannot be obtained. Thus, in the case of producing DVCRs, mechanical design specifications such as a track angle and a tape traveling speed should be strictly observed.
Since there are various kinds of high efficiency coding, the data rate after being subjected to high efficiency coding takes various values. Particularly in pre-recorded soft tapes, etc., the data rate is required to be decreased by high efficiency coding for the purpose of reducing tape cost.
In recent years, studies to supply digital video signals at a very low data rate in video services utilizing a digital TV broadcasting, a CATV, a telephone, etc. have been made. For example, the data rate of DVCRs for broadcasting is very high, i.e., 270 Mbit/s; however, a method for transmitting data after decreasing the data rate to 3 to 12 Mbit/s by filtering, high efficiency coding, etc. and a method for recording data after decreasing the data rate to 25 Mbit/s have been put into practical use. Furthermore, regarding TV signals, in addition to the NTSC system and the PAL system, 1125 line-60 field system and 1250 line-50 field system have been put into practical use.
In the case where a plurality of data rates are obtained depending upon TV signal systems or high efficiency coding methods after coding, a recording method and a reproducing method suitable for each data rate are required.
In general, the recording density and track pitch of the magnetic tape are respectively kept at nearly predetermined levels. Thus, the number of tracks and the tape traveling speed per predetermined period of time are increased in proportion to the data rate. When data is recorded at a data rate different from a normal recording data rate, a signal processing circuit and a device having a completely different cylinder construction are required. It is desired that data in one tape is copied to another tape for a short period of time. In particular, when a great amount of pre-recorded soft tapes, etc. are produced, it is desired to copy data at a data rate higher than normal for a short period of time so as to shorten the time for producing the tapes.